a long slide, H, mounted upon it. This slide is carried on the
crank-pin, I, fastened to the disk, J, attached to the driving shaft, A.
The crank-pin, in revolving, reciprocates the rocking lever, E, and
main piston, F, and through the medium of the pneumatic connection, the
hammer, G. The slide, H, in revolving with the crank-pin, also moves
backward and forward along the rocking lever, approaching the fulcrum,
B, during the down-stroke of the hammer, and receding from it during
the up-stroke. By this means the velocity of the hammer is considerably
accelerated in its downward stroke, causing a sharp blow to be given
while it is gently raised during its upward stroke.

To alter the force of the blow, the hammer, G, is made to rise and fall
through a greater or less distance, as may be required, from the fixed
anvil block, K, after the manner of the smith giving heavy or light
blows on his anvil. It is evident that this special alteration of the
stroke could not be obtained by altering the throw of a simple crank and
connecting rod; but by placing the slot, C, parallel with the direction
of the rocking lever, E, when the latter is in its lowest position, with
the hammer resting on the anvil, and with the crank at the top of its
stroke, this lowest position of the rocking lever and hammer is made
constant, no matter what position the fulcrum, B, may have in the slot,
C. To obtain a short stroke, and consequently a light blow, the fulcrum
is moved in the slot toward the hammer, G; and to produce a long stroke
and heavy blow the fulcrum is moved in the opposite direction.

Fig. 3 gives the details of the pneumatic connection between the main
piston and the hammer, in which packing and packing glands are dispensed
with. The hammer, G, is of cast steel, bored out to fit the main piston,
F, the latter being also bored out to receive an internal piston, L. A
pin, M, passing freely through slots in the main piston, F, connects